A variety of spinal conditions, such as compression of the spinal cord nerve roots, degenerative disc disease, herniated nucleus pulposus, spinal stenosis, and spondylolisthesis may cause moderate to severe lower back and leg pain. Intervertebral or interbody fusion is a surgical procedure that is used to alleviate such lower back and leg pain. In posterior lumbar interbody fusion (PLIF), two adjacent vertebral bodies of the lumbar spine are fused together by removing the affected disc and inserting posteriorly one or more implant devices or cages that allow one or more bone grafts to grow between the two adjacent vertebral bodies to bridge the gap left by the removed disc. Various degrees of distraction may also be provided, as required on a case-by-case basis.
One variation of the traditional PLIF technique is the transforaminal posterior lumbar interbody fusion (T-PLIF) technique. In this surgical procedure, an implant device or cage is inserted into the affected disc space via a unilateral (or sometimes bilateral) posterior approach, offset from the midline of the spine, by first removing portions of the facets of the vertebrae. Advantageously, the T-PLIF technique avoids damage to nerve structures, such as the dura, cauda equina, and nerve roots, but the resulting transforaminal window available to remove the affected disc, prepare the vertebral endplates, and insert the implant device or cage is limited laterally by soft tissue and medially by the cauda equina.
A variety of different implant devices and cages typically used for the traditional PLIF procedure have also been used for the T-PLIF procedure with varying degrees of success. These include threaded titanium, ceramic, and polymer cages, allograft (i.e. bone) wedges, rings, etc. However, as these devices and cages are not designed specifically for the T-PLIF procedure, they are not shaped to be easily insertable into the affected disc space through the narrow transforaminal window, and may require additional refraction of the cauda equina and nerve roots. Such retraction may cause temporary or permanent nerve damage. In addition, some of these devices and cages, such as the threaded titanium, ceramic, and polymer cages, suffer from the disadvantage of requiring drilling and tapping of the vertebral endplates prior to insertion. Further, the incidence of subsidence in long term use is not known for such devices and cages. Finally, the restoration of lordosis, i.e. the natural curvature of the lumbar spine, is very difficult to achieve when a cylindrical or square titanium, ceramic, or polymer cage is used.
Thus, there is a need in the art for an intervertebral implant device for a posterior interbody fusion surgical procedure that is configured such that it may be surgically implanted in the spine of a patient through a minimal access window, thereby sparing and preserving the associated facets to the greatest degree possible.